Beginner Gardening: Basic question about genetics/propagation, 1 by kwanjin

kwanjin wrote:
I was growing MGs in pots outside my backdoor and I dropped some of the seeds into the rocks near them. I noticed a few weeks later that some had germinated. When they got big enough and I knew they would survive, I staked them. Same type of seeds from the same package.

My question(s)...Why are they so different in height? What makes some short and some tall? Is the difference only in the beginning or do some grow naturally smaller than others?